Well, first of all let's make sure the browser you are using is supported. You will find the details here. Click on the OS you are running and on the "Detailed System Requirements" report page, browse the "Supported Software" tab. Scroll down to browsers and make sure your browser and version is listed there as supported.

In this case, the browser used was IE8, so it was supported. Good.

A quick test is to clear the browser cache, delete cookies and temp files and try again.

If it still fails after that, you might have the Google Chrome Frame Plugin installed on your system. This plugin can be causing these login issues.

To verify if this plugin is installed, browse your Control Panel > Add/Remove Programs

Once you have removed it, you might need to reboot your workstation for the change to take effect. After the reboot, try to open PD again.

This should have solved the problem.

And if it did not, take two of these and call me in the morning.
Yours,